High performance quasi-isotropic thin-ply carbon/glass hybrid composites with pseudo-ductile behaviour loaded off-axis

Mohamad Fotouhi,Meisam Jalalvand,Milad Saeedifar,Bill Xiao,Michael R Wisnom

doi:10.1016/j.compstruct.2020.112444

Abstract

The aim of this work was to investigate the effect of loading angle variation on the pseudo-ductility of quasi-isotropic (QI) hybrid composite laminates. Previously, hybrids of thin-ply carbon fibres and standard glass fibres were found to have an excellent pseudo-ductile behaviour both in unidirectional (UD) and QI configurations when subjected to axial tension in the fibres’ orientations. In this work, the QI laminates, with 60° intervals, have been subjected to a quasi-static tensile load at various off-axis orientations – i.e. 5°, 10° and 20°. The QI hybrid composites were made by sandwiching a QI T300-carbon laminate between the two halves of a QI S-glass laminate. The results showed a pseudo-ductile behaviour with a linear elastic part and a desirable plateau for all the loading directions, however the pseudo-ductile strain decreases when increasing the off-axis angle. Comparing the 20° off-axis with the other cases, there was more active matrix cracking damage before fragmentation in the 20° off-axis plies and it failed earlier than the other samples. Acoustic emission (AE) results confirmed this, with more matrix cracking related AE signals in the 20° off-axis case compared to the other configurations.

Highlights

Advanced composites are frequently used in strength-critical applications where often the direction of loading is unknown, so even if multiple plies are included in a composite plate, it can be loaded offaxis, compared to the direction of its fibres
The results showed that these hybrids can generate pseudo-ductility when loaded in tension in the off-axis orientations as well as the all fibre orientations
This paper investigated the effect of loading angle variation, (i) along the different fibre orientations, i.e. 0°, 60°, −60°, and (ii) at different off-axis orientations – i.e. 5°, 10° and 20°, on the pseudoductility of QI hybrid composite laminates, consisting of thin-ply carbon T300/standard thickness S-glass prepregs, and the following conclusions are drawn:

Summary

Introduction

Advanced composites are frequently used in strength-critical applications where often the direction of loading is unknown, so even if multiple plies are included in a composite plate, it can be loaded offaxis, compared to the direction of its fibres. Previous studies [1,2] demonstrated that due to edge effects, a QI laminate (elastically isotropic in the laminate in-plane) can be highly anisotropic in strength. It was observed that the failure modes change if the loading direction deviates slightly from one of the fibre orientations. These failure modes can combine to produce catastrophic failure and can decrease strength of the composites drastically. In another study [3], the occurrence of damage in a lay-up was studied by examining various orientations of a particular ply without changing the orientation of the others. Matrix cracking was observed in the ply under transverse tension stresses and the laminate elastic moduli underwent changes with crack density

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